Following a request from the European Commission, the Panel on Plant Protection Products and their Residues (PPR) was asked to deliver a scientific opinion on the report of the FOCUS groundwater working group (FOCUS, 2009) with respect to lower tier leaching assessments.
The PPR Panel is of the opinion that robust and efficient risk assessment processes are facilitated by specific definitions of protection goals. To this end, the PPR Panel recommends that assessment goals in respect of leaching of plant protection products are clarified, in particular to confirm that protecting the drinking water function of the groundwater should be the specific protection goal.
The PPR Panel is of the general opinion that the FOCUS groundwater working group has successfully harmonised major concepts in the leaching models and that, overall, the leaching estimations have improved. The PPR Panel however disagrees with the FOCUS working group on submitting calculations with only one model and recommends that decisions continue to be based on more than one model. Despite several limitations, the PPR Panel considers that the revised FOCUS scenarios cover significant arable areas in the EU, including the New Member States, and allow for decision making at the EU level.
Potatoes are included in all of the nine FOCUS scenarios. As the currently approved leaching models are not capable of calculating leaching from ridge/furrow systems correctly, the PPR Panel considers the inclusion of potatoes not warranted without accounting for the potential underestimation of the leaching. In absence of an appropriate model, applying a safety factor may temporarily solve the problem. The PPR Panel recommends reconsidering the leaching assessment for potatoes.
The PPR Panel is aware that the original intention of the FOCUS WG (FOCUS, 2000), i.e. to cover approx. 80 % of the arable area in the EU (at that time the EU-15) with the nine FOCUS scenarios, is no longer met for the entire EU-27 (approx. 65 % of the arable area in the EU-27 is considered to be covered). Taking into account limitations of the scenarios stated below (e.g. areas with preferential flow not accounted for) the actual covered arable area by the FOCUS scenarios is likely to be even smaller. Nevertheless, the PPR Panel is of the opinion that the arable area in the EU covered by the FOCUS scenarios is still significant.
The PPR Panel considers the leaching assessment proposed for Tier 1 consistent with the state of the art at that time. However, in the meantime new guidance and opinions were published by EFSA in respect to model input parameter estimation (e.g. DegT50, KOM, crop interception) and model procedures (wash-off from crop surface, etc.). The PPR Panel recommends taking the new EFSA guidance into account as soon as is practicable.
The PPR Panel recognises that the scenario selection procedure is not in line with recommendations by EFSA (2012a). This is particularly true for the selection of the scenario location in respect to soil vulnerability, which at that time was based on expert judgement only, without spatial analysis of soil maps. Also, the FOCUS scenarios neither account for uncertainties in substance properties nor for different areal distribution of crops within a scenario, which may have a significant impact on the spatial target percentile. In this respect the consistency of the tiered approach in introducing spatial soil data at higher tiers as proposed by the FOCUS WG cannot be ensured.
With the exception of one scenario (Châteaudun), the current FOCUS groundwater assessment approach does not account for potential preferential flow through the soil. The one scenario for which potential preferential flow is calculated is merely there for raising the awareness of risk assessors and risk managers to the phenomenon so it can be accounted for in assessments at the national level. There is ample evidence that preferential flow may be an important aspect of downward movement through the soil. The PPR Panel recommends reconsidering the impact of preferential flow on the groundwater leaching assessment, taking into account new knowledge available to account for such processes based on basic soil properties. However the quality and the accurateness of pan EU soil maps (e.g. soil organic matter, pH and texture) have to be considered.
The PPR Panel recognises the efforts of the FOCUS WG to harmonise the dispersion length, water balance and water movement aspects between the models, based on best knowledge available, and that the various approaches used by the models are no longer a major source of differences in calculation results. The PPR Panel is of the opinion that further progress can be made once better data on irrigation (in particular in Southern Europe) become available.
Two of the scenarios, Piacenza and Porto, were revised in order to meet the target percentile leaching concentration of the respective climatic zone. In principle, the PPR Panel agrees on the procedure proposed by the FOCUS WG to change the vulnerability of these two FOCUS scenarios, as it was the best available option at the time. However, methods have recently become available that permit development of scenarios with a certain target vulnerability.
The PPR Panel also noted that additional changes were made to the scenarios which were outside of the remit of the FOCUS GW. This is in particular true for the soil pH, which was made available within the model shells in order to account for pH depending substance properties.
The PPR Panel considers that the spatial analysis performed by the FOCUS WG to check the suitability of the FOCUS scenarios for the New Member States were state of the art in respect to the methodology and data bases available at that time. It may be noted that results of this analysis have to be considered preliminarily only, since only topsoil characteristics were taken into account. Inconsistencies with the maps used (e.g. the OCTOP map) are known. In the meantime better tools have become available now. The PPR Panel is of the opinion that the current set of FOCUS leaching scenarios is also applicable to New Member States at least for the purpose of Tier 1 screening simulations.
The PPR Panel considers the version control procedure for FOCUS tools adequate in principle. The PPR Panel recommends that thorough evaluation and testing of new versions of models, databases and user interfaces before release is continued. However, the voluntary basis on which the testing of models is based makes the procedure vulnerable. It is recommended to institute more binding provisions for these activities to minimise risks arising from poor version control and to ensure the availability of robust and trustworthy scenarios and software tools also in the future.
The PPR Panel has observed that problems in the underlying soil data have become clear after finalising the report. Also new approaches on scenario selection have become available. The PPR Panel recommends that these flaws and new approaches are taken into account when developing revised scenarios. This implies consideration of uncertainties in substance properties and implementation of crop extrapolation factors as well. It is also recommended to reconsider soil pH to allow adequate leaching assessments for compounds showing pH-dependent properties.
An in-depth review of irrigation efficiencies and practices, in particular in Southern Europe, is recommended as currently 100 % efficiency is assumed.